Cell Reproduction Why do Cells Divide? Section 5-1, 5-2 Why must the cell divide? Nutrients and waste pass through the cell membrane When the cell membrane no longer has a large enough surface area to transport the volume of the cell It divides! How long do our cells last? In the human body our cells last between two weeks (a skin cell) to 16 years (our muscles) Cell division occurs more rapidly in embryos and children The Cell Cycle Interphase The longest phase of the cell cycle G 1 phase the growth phase, organelles increase in number, longest phase of interphase S phase chromosomes are replicated G 2 phase- cell continues to grow What is a Chromosome? Mitosis The Division of Chromosomes Specifically the chromosomes in somatic cells Prophase Chromosomes shorten and thicken Nuclear membrane disappears Spindle fibers form Centrioles move to opposite poles Metaphase Chromosomes line up at equatorial plate Attach to spindle fibers with centromere Anaphase Chromosomes move towards poles Telophase Nuclear membrane forms around chromosomes Cytokinesis The division of the cytoplasm The cell membrane forms between the two new identical daughter cells